In general, stable emulsion systems require the use of surfactants to reduce the surface energy at an interface between a water phase and an oil phase. Many such surfactants, or emulsifiers, are known. Some types of emulsifiers, more than other types, create emulsions of greater stability. For example, it is well known that O/W emulsions achieve greater stability if the emulsifier is anionic, that is a lipophilic tail attached to a hydrophilic end-group, the end-group having a net negative charge. A number of lipophilic tails surround and align in the direction of an oil droplet while the hydrophilic end groups extend out into the continuous water phase, away from the oil droplet. Thus, the outer most surface of the droplet complex is negatively charged. This causes droplets to repel each other and inhibits their coalescence, which would otherwise destabilize the emulsion. As an example, a formula for a stable emulsion with anionic emulsifier is shown in table 1. One drawback of this type of emulsion stabilization is that the anionic emulsifier cannot be introduced into the system by simple addition. Rather, the anionic emulsifier must be formed in situ. This is generally done by adding a non-polar precursor to the oil phase and a polar precursor to the water phase. Another drawback is that water-in-oil (W/O) emulsions cannot be stabilized in this manner.
TABLE 1percentwater58.05glycerine6.00sodium stearoyl glutamate2.60(anionic emulsifier)disodium EDTA0.10phenoxyethanol0.25isononyl isononanoate3.00denatured alcohol15.00dimethicone15.00
On the other hand, cationic emulsifiers are not generally used to stabilize an O/W emulsion. So, for example, an O/W emulsion having the formula shown in table 2, (the same as table 1, except for the emulsifier) is not stable at room temperature, even over a relatively short time. For this reason, cationic emulsifiers are not generally included in O/W emulsion systems.
TABLE 2percentwater58.05glycerine6.00isostearamidopropyl dimethylamine2.60(cationic emulsifier)disodium EDTA0.10phenoxyethanol0.25isononyl isononanoate3.00denatured alcohol15.00dimethicone15.00
Non-ionic emulsifiers may also be used to increase emulsion stability. Non-ionic emulsifiers introduced into an emulsion by simple addition will migrate to the water-oil interface and lower the interfacial energy, thereby making the emulsion more stable. Low HLB non-ionic emulsifiers will generally stabilize W/O emulsions, while high HLB emulsifiers will generally stabilize O/W emulsions. Table 3 is an example of a stable O/W emulsion using non-ionic emulsifiers.
TABLE 3percentwater72.80glycerine6.00phenoxyethanol1.00glyceryl stearate3.00(non-ionic emulsifier)cetyl alcohol2.20(non-ionic emulsifier)dimethicone15.00
Conventional Incorporation of Hydrophobic Agents—
It is well known that if hydrophobic agents are to be incorporated into O/W emulsions, the hydrophobic agents should be added to the oil phase prior to forming the emulsion. This is true in general and specifically of those color cosmetic emulsions that employ hydrophobic pigments. Generally, adding the hydrophobic agents to a preformed emulsion does not work, as the hydrophobic agents are not miscible in the external aqueous phase. For example, when hydrophobic pigment was added to the stable preformed O/W emulsion of the formula shown in table 1 (having anionic emulsifier), the result was that the pigment could not be dispersed and the composition was not stable. The same is true when hydrophobic pigment was added to the stable, preformed O/W emulsion of the formula shown in table 3 (having nonionic emulsifier).
Conventionally, when an O/W application calls for hydrophobic pigments, a pigment grind is made in advance and thereafter dispersed in an oil phase, prior to forming an emulsion. A typical pigment grind may comprise a simple mixture of hydrophobic pigment, oil and lecithin. The liquid portion of the grind “pre-wets” the pigments, making their incorporation into the oil phase easier. Alternatively, sometimes it may be possible to pre-treat a hydrophobic agent to make the agent “less hydrophobic,” but this pretreatment step may not be desirable for a number of reasons. Pretreatment adds cost. It may interfere with the effectiveness of the hydrophobic agent. It may render the composition irritating to the skin. Such pretreatments are not available in all cases where one might like to use a hydrophobic ingredient. The present invention avoids these difficulties.
Generally, the internal phase droplets do not all have the same diameter, but the emulsion may be characterized as a range of droplet sizes about an average diameter. Emulsions are somewhat imprecisely classified based on the internal phase droplet size and on whether the emulsion is monodisperse or polydisperse (i.e. having one or more peak droplet diameters). For example, macroemulsions, which are typically opaque with milky-white appearance, comprise particle sizes larger than about 200 nm. In a microemulsion, the average droplet diameter is between 10-200 nm, while nanoemulsions have an average particle diameter less than about 10 nm. Other sources may place the boundary between macro and microemulsions at about 50 or 100 nm. Other sources maintain that nanoemulsions have larger droplet sizes (50-200 nm) than microemulsions (5-50 nm), the distinguishing feature having more to do with the type of stability (i.e. microemulsions are thermodynamically stable while nanoemulsions are kinetically stable). At any rate, because of their small droplet size, nanoemulsions and microemulsions are generally clear. Microemulsions and nano emulsions typically employ an aliphatic alcohol as co-surfactant and it is known that the average oil droplet size in an O/W emulsion depends on the ratio of alcohol to other surfactant in the system. Increasing the ratio of alcohol to surfactant decreases the average oil droplet size, which also increases the dispersion of the oil droplets and uniformity of the internal phase.
Benefits and Drawbacks of O/W and W/O Color Cosmetic Emulsions—
Turning specifically to color cosmetic compositions, foundations and other color products may be implemented as W/O or O/W emulsions, each having strengths and weakness. O/W makeup emulsions have better mass to skin tone properties than W/O makeup emulsions. By “better mass to skin tone properties”, we mean that the color of a makeup applied to skin more closely matches the color of the same makeup sitting in a container at ambient conditions. O/W makeup emulsions generally feel lighter, cooler and less greasy than W/O makeup. They are also, easier to remove. Furthermore, O/W systems generally have better break on the skin, i.e. the makeup spreads more easily and more evenly. On the other hand, W/O makeup emulsions have better or longer wear characteristics than O/W makeup emulsions, which often include a film former to improve wearability. W/O makeup emulsions also hold up to moisture better than O/W emulsions. The developer is faced with this trade-off between truer color and feel on the one hand and long wear on the other. A simple, inexpensive method for achieving the best of both in a single emulsion is unknown in the prior art. This is unlike the present invention wherein the superior wear of a W/O emulsion makeup is combined with the pleasant aesthetics and truer color of an O/W emulsion makeup.
Conventionally, the type of pigments used to impart color determines the type of emulsion used to implement the makeup. If hydrophobic pigments are used, then the emulsion is a W/O emulsion, having the pigment dispersed in the external, oil phase, prior to emulsification. To avoid agglomeration of the pigment and ensure a good dispersion in the final emulsion, the hydrophobic materials may be prepared as a sub-phase called a grind. In the grind, pigments are pre-treated or “wet” to assist their incorporation into the emulsion. For example, for incorporation into an O/W emulsion, the pigment may be pretreated with lecithin and oil. The grind is subsequently added to the oil phase of the emulsion, prior to forming the emulsion and mechanical mixing or shearing means are employed to aid the dispersion of the pigments. In contrast, the pigment of the present invention is pretreated in a novel manner, and the pretreated pigment is added to the base emulsion, after the base emulsion has been formed.
CAN-Type Emulsions—
Ternary blend emulsifier systems are known. U.S. Pat. No. 6,528,070 (herein incorporated by reference, in its entirety) describes a so called “CAN” emulsifier system. This ternary emulsifier system comprises a cationic (the “C” in CAN), an anionic (the “A” in CAN) and a bridging surfactant. The bridging surfactant may be a non-ionic surfactant, hence the “N” in CAN. However, the bridging surfactant may also be an amphoteric surfactant or an ethoxamide. The bridging surfactant acts as a bridge between the cationic and anionic surfactants. The reference discloses the ratios and concentrations of each emulsifier for which the final emulsion is stable. Disclosed are emulsions in which the CAN emulsifier system comprises from 0.3% to about 15% of the emulsion and wherein each of the cationic, anionic and bridging surfactants form about 0.1 to about 8.0% of the weight of the emulsion. Further disclosed are CAN-type emulsions comprising particulate matter, as for example, sunscreens at 0.1% to 10% on a weight basis. The particulate matter may be, for example, inorganic sunscreens, powders, pigments, abrasives, coal tar, anti dandruff agents or a mixture thereof. This emulsifier system is described as being particularly useful in making stable O/W emulsions without the use of additional hydrophilic groups (such as ethylene oxides) on the anionic or cationic surfactants.
Furthermore, according to the reference, the emulsions and suspensions disclosed can be made by combining the ingredients in any order. Also, the reference briefly mentions that hydrophobic materials may be incorporated into CAN-type emulsions. Taken together, this would seem to indicate that a stable emulsion system can be arrived at by adding a hydrophobic material to a preformed O/W emulsion. Concerning example 8 of the '070 reference (shown below in table 4) it is said that “a stable o/w emulsion was obtained when the anionic, cationic, bridge system (1:1:1 mole ratio) was used as an emulsifier system for a sunscreen formulation.” This formula is purported to be stable at 25.degree. C., 43.degree. C. and 50.degree. C., for at least thirty days. The reference does not explain how the sunscreen was made, that is, was the hydrophobic titanium dioxide (Micro LA-20) added to the oil phase, in a conventional manner, or was it added to the preformed O/W emulsion? Applicants performed the following experiment. Column three of table 4 is identical to example 8 of the '070 reference, except for the substitution of CAN-emulsion systems. The formula in column 3 was prepared in two ways; adding the hydrophobic pigment to the oil phase and adding the hydrophobic pigment to the preformed CAN-type emulsion. In either case, the emulsion was stable at ambient conditions for at least one month. So indeed, in this specific case, adding a hydrophobic material to a preformed O/W CAN-type emulsion was possible. However, as we shall see, the formula of example 8 of the '070 reference and the formula of table 4, column 3 do have limitations that are not readily disclosed in the '070 reference.
TABLE 4Ex. 83456percentpercentpercentpercentpercentTotal CAN system1.71.71.71.71.7Anionic surfactantx(STCS370)Cationic surfactantx(BTC65NF)Bridge surfactantx(AMXLO)Anionic surfactantxxxxCationic surfactantxxxxBridge surfactantxxxxElefac I-2051515151515Kessco1515151515octylisononanoateMicro LA-201010untreated TiO2Alkyl silane pigment10fluoro alcoholic10phosphate pigmentdimethicone treated10pigmentCarbopol Ultrez 100.30.30.30.30.3waterqs100qs100qs100qs100qs100stablestableunstableunstableunstable
Acting against the teachings of the reference, applicants conjectured that there may be limitations not disclosed in the '070 reference. Applicant's undertook the following action. Column 4 is identical to column 3 except for the substitution of alkyl silane pigment for Micro LA-20 (hydrophobic titanium dioxide). The formula of column 4 was prepared by adding the hydrophobic material (Alkyl silane pigment) to a pre-formed CAN emulsion. The resulting product is not stable after any amount of time. This result was also achieved when the alkyl silane pigment was replaced with a fluoro-alcoholic phosphate pigment (column 5) or with a dimethicone treated pigment (column 6). In other words, the '070 reference is overly broad in its implications that hydrophobic materials can be incorporated into O/W CAN-type emulsions by combining the ingredients in any order. In fact, as just shown, it is not generally possible to add hydrophobic materials to a pre-formed O/W emulsion, even a CAN-type emulsion. The hydrophobic material hits the external water phase and thereafter does not find a stable arrangement in the system. Furthermore, even if hydrophobic materials had been added to the oil phase of the CAN O/W emulsion, prior to forming the emulsion, the resulting composition is not necessarily stable and not necessarily of a suitable quality. The use of a CAN-type emulsion system as described in the '070 reference does not guarantee that hydrophobic materials can be stably dispersed in an O/W emulsion. In contrast, the applicants have discovered a modified method for stably dispersing hydrophobic materials in CAN-type O/W emulsions.
That the formula of example 8 of the '070 reference could be made by adding the hydrophobic titanium dioxide to the pre-formed O/W CAN-type emulsion may have to do with the fact that the specific titanium dioxide (Micro LA-20, from Grant Industries, Elmwood Park, N.J.) is pre-treated in aluminum hydroxide (and) lauric acid. Aluminum hydroxide (and) lauric acid is an acid salt and known non-ionic surfactant. As discussed above, non-ionic emulsifiers introduced into an emulsion by simple addition will migrate to the water-oil interface and lower the interfacial energy, thereby making an emulsion more stable. So, a careful reading of the '070 reference confirms that there is no general method disclosed for incorporating hydrophobic materials into a preformed CAN-type O/W emulsion. In contrast, the present invention includes compositions and methods for stably dispersing hydrophobic materials into preformed CAN-type O/W emulsions.
Furthermore, as mentioned above, the '070 reference discloses that stable emulsions are formed when the CAN emulsifier system comprises from 0.3% to about 15% of the emulsion and wherein each of the cationic, anionic and bridging surfactants form about 0.1% to about 8.0% of the weight of the emulsion. The reference includes examples wherein the bridging surfactant is as low as 0.31% of the weight of the emulsion. Based on this, a person of ordinary skill in the art could not be expected to find a novel use for a CAN-type surfactant system wherein the bridging surfactant is 0.05% or lower. Nevertheless, the applicants have done so.
Objects
A main object of the present invention is to provide compositions having one or more hydrophobic agents stably dispersed in an O/W emulsion.
Another object of the present invention is to provide compositions that combine the aesthetic properties of O/W emulsions and the long-wearing properties of W/O emulsions.
Another object is to provide a method of making compositions that have one or more hydrophobic agents stably dispersed in a base O/W emulsion, wherein the step of dispersing the hydrophobic agents takes place after the base emulsion is formed.
Another object is to provide a novel method of pre-treating hydrophobic agents for dispersing in O/W emulsions.